Day Three: Barlow Assembly, Tripod and Daytime Observations

Getting Ready
You should practice putting together the Galilean eyepiece. It has very small lenses and is frequently the most difficult part of the assembly process. You should practice focusing the Galilean eyepiece. You have to push the focuser in farther with the Galilean eyepiece. You will notice that the Galilean eyepiece gives a right side up view. You will notice that the field of view is very small, however, making it difficult to use. The Galilean eyepiece is not suitable for astronomical observing, but it does illustrate the difficulties Galileo had to deal with.

Practice assembling and focusing the Barlow lens. Focusing the Barlow lens is more difficult than the Plossl lens. There is a very narrow range where you will get a clear image. You will notice the image is dimmer with the Barlow lens. Since the magnification is higher, you are spreading the light over a larger area resulting in a dimmer image. Using the Barlow lens gives a smaller field of view as well so objects are more difficult to find. The Barlow lens is used primarily for looking at bright, easy to find objects where you want higher magnification.

Practice mounting the Galileoscope on the tripod. The ¼-20 nut should fit any standard camera tripod. The exact procedure you use depends on the tripod you have.

In Class
Hand out the telescopes and pieces left over from the day before. Lead the students through the process of assembling the Galilean eyepiece. Show the students how to use the Galilean eyepiece. Note the narrow field of view. Make sure they understand that this is NOT a good observing mode, but it does show them what Galileo had to use.

Next assemble the Barlow so the students can see a 50x view. The focus is more difficult in this configuration (you have a very small range where the focus is good compared to using the main eyepiece by itself). The image will not be as bright using the Barlow. The Barlow is useful only for bright objects where you want a higher magnification. Your main targets with the Barlow will be the Moon, Jupiter and Saturn. Most other objects look better using the main Plossl eyepiece.

Be sure the students understand all three observing modes and have them practice switching from one to the other several times.

Next you want to show the students how to mount the Galileoscope to a camera tripod. It is important to learn this skill during the day when you have good light (rather than trying to learn it at night in the dark!) A tripod will be necessary to steady the telescope during observations. The Galileoscope will mount to any standard camera tripod. The exact technique depends on the model of tripod you are using.

Have the students practice pointing the Galileoscope at targets during the day. There is a site on the top of the tube. It is important to practice this skill during the day so you are good at pointing the telescope when you go out at night (it is always more difficult in the dark!)

NOAO is the national center for ground-based nighttime astronomy in the United States and is operated by the Association of Universities for Research in Astronomy (AURA). under cooperative agreement with the National Science Foundation.